Carburetor



June 8, 1954 R. F. BRACKE 2,680,605

CARBURETOR Filed Oct. 20, 1950 2 Sheetssheet 1 I 3 y/wyev/vivv 1 1125 j gg/a0 120 30 114 29M, [fl-WQ /f-,f/ f/d/ June 8, 1954 R F BRACKE 2,680,605

CARBURETOR Filed Oct. 20, 195() 2 Sheens-Sheei'l 2 Patented June 8, 1954 CARBURETIOR Robert F. Bracke, Arlington Heights, Ill., assignor,

by mesne assignments, to R. F. Bracke & Company, Chicago, lll., a partnership composed of Hazel B. Bracke and Robert Anderson Application October 20, 1959, Serial No. 191,260

4 Claims. 1

My invention relates to carburetors and is more particularly concerned with, but not necessarily limited to, a compact, Simple, inexpensive, and eicient carburetor especially adapted for small tools and similar uses and capable of operating eiectively in all positions.

An object of my invention is to provide such a carburetor having a new and improved diaphragm arrangement for controlling the fiow of fuel.

A further object of my invention is to provide such a carburetor having a new and improved arrangement of fuel passages.

Another object of my invention is to provide a multi-jet carburetor having new and improved means for preventing back-bleed.

Still another object of my invention is to provide a carburetor having a new and improved air valve.

Another object of my invention is to provide a new and improved carburetor wherein the number of close tolerances is reduced to a minimum and which accordingly can be manufactured inexpensively by mass production methods.

Other objects and advantages will become apparent as the description proceeds.

In the drawings:

Fig. l is a sectional elevational View of a preferred embodiment of my invention;

Fig. 2 is an enlarged sectional view of the Valve means for preventing back-bleed; and

Fig. 3 is an assembly view largely in vertical section showing a modied form of my invention and its associated fuel tank.

Referring iirst to the embodiment of Figs. 1 and 2 it wil be seen that I have illustrated a carburetor having a main body lil providing an air inlet I2 communicating with a choke bore i4 containing the usual choke valve i6. A venturi i8 is between the choke bore it and throttle bore 20, the latter containing a throttle valve 22.

Fuel is supplied to the carburetor through an inlet 24 communicating with a chamber 25 immediately beneath the main fuel valve 28 which controls communication between the chamber 26 and passages leading to the main fuel jet 3i), idle jet 32, and orice 34. The valve 28 is of fruttoconical shape and may be integral with or atn tached to a valve stem 35 which is urged upwardly by a spring 33 tending to seat the valve 28 on a knife edge 46 provided by a valve seat member 42. The spring 3S is interposed between a shoulder 44 provided by the valve seat member 42 and a pin i6 extending transversely through and projecting from both sides of the valve stem 36.

The fuel valve 23 is moved to open position by a pair of diaphragme 43 and 5t located respectively in diaphragm chambers 52 and 54. The diaphragm chamber 52 is formed between the cupped upper end of the carburetor body I0 and the web 56 of a spacer ring 58, whereas the diaphragm chamber 54 is formed between the web 56 and a cover 60. The spacer ring 53 and cover 60 are secured to the body It by screws 62 and 64.

The diaphragm 48 is formed of a specially treated material which is impervious to gas, gasoline, and oil, and which has a certain amount of flexibility permitting the central part of the diaphragm to move in a vertical direction while the periphery of the diaphragm is iirmly clamped between the spacer ring 53 and the upper end of the body I0. The central part of the diaphragm 48 is provided with oppositely disposed metal plates 63 and t8 secured to the diaphragm 48 by a rivet l0. The lower face of the rivet i9 rests upon the upper end of valve stem 35 but a spring 'l2 interposed between plate 6B and shoulder M prevents this rivet from exerting any downward force on valve stem 36 as a result of the action of gravity on diaphragme 48 and 59 and push rod 16.

The upper diaphragm 53 may be of the same construction as the lower diaphragm 48. The periphery of diaphragm 50 is firmly clamped between cover 66 and spacer ring t8 and the rivet i8 which clamps metal plates til and 82 to the central portion of this diaphragm rests upon the upper end of push rod it. The upper sides of the diaphragms are in open communication with each other and with atmosphere by way of passages li, 8S, 88, 90, 32, and 9e, the latter three passages being provided in the special screw Bt. The upper diaphragm 59 is a dry diaphragm and its lower side is in communication with venturi i8 by way of passages t6, St, and |69. The lower diaphragm 48 is a wet diaphragm and has its lower side in communication with the fuel passages in a manner which I shall hereinafter describe.

The fuel valve 23 controls flow of fuel from the chamber 26 to a second cham :er E62 formed in the valve member 42. This second chamber communicates with the main jet 3Q by means of passages |04, 106, it, and valve chamber Ht. A needle valve I l2 may be adjusted to regulate the amount of fuel delivered by the jet St and this needle valve is held in adjusted position by a spring H4. The valve chamber itil and valve structure therein is vshown more clearly in Fig. 2.

The valve chamber I I is formed in a two-diameter hollow plug ||2 which is threaded into the body i0 and has its lower end closed except for the jet 3i) by a disc il press iitted and driven into the plug |12. This plug provides an annular valve seat H5 adapted to be engaged by a valve member H8 when the latter is raised by reverse flow, that is, iiow of air into the iet 3i). The valve member |i8 is a free disc of thin material such as metal or cloth and normally rests on the raised ends of a support so that fuel may flow freely down passage IES and around valve member H8 to jet 30.

Fuel chamber |62 also communicates with idle jet 32 and oriiice 136 to supply fuel thereto. This communication is by Way of passage |24, valve chamber |25, and passages |28, |39, and |32. The upper end of passage E24 communicates with diaphragm chamber 52 beneath diaphragm 53.

A. feature of my invention lies in the particular means for admitting additional air when the engine is operating at high speed full throttle, thus giving the effect of an expandible carburetor. The lower part of the carburetor body IB is formed to provide an elongated vaive chamber |34 closed by a cover |36 secured to the main ybody ii] by screws |38 and having a suitable sealing gasket |550. A port |42 connects one end of elongated chamber E35.- with the choke bore i4 and a second port Mii connects the other end of the valve chamber with the throttle bore 29. Within the chamber |34 is a reed valve M5 secured at one end to body iii by screw |48.

The valve |136 may be made of thin sheet steel or other suitable resilient material and normally lies in the full line position shown in Fig. 1. In this position it closes the port |i2 to prevent ow of air through this port and into charnber i3d. However, when the differences in pressure between the choke bore id and throttle bore 2G become suciently great, the suction in chamber i3d causes the free end of the valve M6 to flex downwardly as indicated in dotted lines to admit additional air to the engine.

it will be understood of course that the cari buretor is intended to be attached to the intake port or manifold of an engine in any suitable manner and that fuel inlet 2e is to be connected to a suitable source of fuel supply. If desired, an air lter may be attached to the inlet end of the carburetor. Preferably, the source of fuel supply is either a fuel pump or a tank located slightly above the carburetor and feeding thereto by gravity.

In operating my novel carburetor, needle valves H2 and i253 are opened from one-half to three-fourths of a turn, and if the engine is cold, the choke valve it is closed or partly closed to enrich the starting mixture; the throttle valve 22 would be partly opened; the engine is cranked and produces a ilow of air through the carburetor. Suction caused by this flow of air through venturi iS is conducted by means of passages iti), 98, and et to the lower side of diaphragm 59, with the result that this diaphragm is moved downwardly by the atmospheric pressure thereabove and opens fuel valve 28. Thereupon fuel flows past this valve and through the short passages communicating with the jets 3c and 32 and oriiice 32. This opening movement of the fuel valve 28 is also aided by diaphragm i8 since the lower side of this diaphragm comvmunicates with high speed jet 3e by way of passages lt, |2, |011, lil, |03, and valve chamber Iii 0. If the choke valve is closed or partly closed during the starting operation, this valve is returned to fully open position as soon as the engine warms up. The throttle valve 22 of course is adjusted to give the desired speed of engine operation under the load imposed thereon.

It will be noted that the upper sides of both diaphragms i3 and 5) are at all times exposed to atmospheric pressure. The lower side of the upper or dry diaphragm 5G communicates with the venturi I6 so that the pressure beneath this diaphragm reects the suction created in the venturi i8 by the iiov/ of air therethrough and thus varies with engine demand. The lower diaphragm acts as a pressure regulator since the space therebeneath is filled with fuel. This diaphragm tends to vary in accordance with fuel pressure and gives automatic compensation for variations in the fuel pressure at the fuel intake of the carburetor.

The size of the ports M2 and IM and the spring tension of the reed valve |1165 are such that this vaive remains closed during the starting operation and even when the engine is operating at lowest speed with wide open throttle valve. However, if the engine speed at Wide open throttle is increased, as, for example, by decreasing engine load, the reed valve fiii flexes downwardly to permit additional air to bypass venturi i8 by iiowing through port U32, chamber |34, and port li to the throttle bore. This opening of the reed valve is produced by the increased suction at the higher engine speeds and the suction deflects the free end of the reed valve away from port |52. This arrangement produces in effect an expandible carburetor since it gives in the wide open range an air valve carburetor, without, however, giving the extreme sensitivity of mixture quality produced by an air valve carburetor at the idling and other low speed part throttle running conditions.

From the foregoing description of the construction and mode of operation of my carburetor, it will be seen that have provided a novel carburetor having one wet diaphragm and one dry diaphragm both cooperating to control the fuei valve. This arrangement is advantageous in providing more opening force and permits the use of a stiffer valve spring to provide a more positive valve-closing action. Furthermore, the two diaphragme in eifect separate two functions while combining the effects of these two functions to aiord a more accurate control of the fuel valve. One of these functions is compensation for variation in fuel pressure at the carburetor inlet due to variations in pump pressure or variations in fuel level in a gravity system. The other function is compensation for variations in engine demand. In this connection I wish to point out that the dry diaphragm connects with the point of highest suction and flexes more rapidly than the wet diaphragm to respond to engine acceleration and other variable conditions of engine operation.

I also wish to call attention to the simplicity of the fuei valve control and the fact that the frusto-conical valve and its seat are the only parts requiring precision manufacture. The pin 'i6 may form a relatively sloppy t in the web 5B and the other parts of the fuel control assembly may be readily made on conventional high production equipment within tolerances suitable for such equipment.

Another feature of my invention lies in the arrangement of the parts whereby the fuel valve is located close to the jets 3i? and 32 and orifice 94 so that variations in the effect of gravity on the operation of the carburetor when the latter is inverted is held to a minimum. Also, the passages connecting the fuel inlet with the delivery points are short and without unnecessary restrictions so that the fuel may flow freely therethrough except to the extent that it is controlled by the needle valves.

Another feature of my invention lies in the provision of the check valve H9 and its associated structure. This check valve is located in the fuel supply line to the main jet 30 but in no wise interferes with flow of fuel t0 that jet. On the other hand, this check valve closes instantly upon the creation of a condition which would tend to cause back-bleed through the high speed jet and thereby insures accurate metering of the fuel and smooth operation when the throttle valve is in idle position or only slightly opened.

In Fig. 3, I have shown an assembly utilizing a simplified and less expensive form of my novel carburetor. In this figure I have shown a carburetor having a body |50 provided witha choke bore |52 having the usual choke valve 54 mounted therein. The carburetor also has a throttle bore |56 provided with a conventional throttle valve |58. Between the two bores is a simplified restriction |60 in the form of a plate |32 having a central orifice. The plate |92 may be press fitted or otherwise secured in the body of the carburetor.

Communicating with the throttle bore are three orices |64, |96, and |68, all of which connect with the passageway |10. Leading into the passageway |70 is an orifice |12 forming a valve seat for a needle valve or other adjustment valve |74. A valve chamber |16 connects the orince |72 with passage |19 and threaded inlet E39 adapted to receive the fitting |182 of a fuel line 85 which extends downwardly and into the fuei supply reservoir |36. This reservoir is preferably shallow and located immediately beneath the carburetor to minimize the fuel lift and variations in fuel head in the reservoir. The reservoir may be vented as indicated at 88.

An elongated valve chamber |90 is parallel with the main axis of the carburetor and has openings or ports |92 and |94 connecting this valve chamber with the choke and throttle bores respectively. Attached to the carburetor body by means of a screw |96 is a reed valve |98 so arranged that it normally lies iiat as shown and covers or seals the port 492 to prevent flow of air from the choke bore through the reed valve chamber and thus into the throttle bore.

If desired, means may be provided for adjusting the spring tension of the reed valve |98. Such adjusting means may assume various forms but in the particular embodiment shown this means is illustrated as composed of an adjusting screw 200 threaded into the cover 202 and serving to vary the compression of a coil spring 204 interposed between the screw 200 and the free end of the reed valve |98. In this arrangement the screw 200 is a high speed adjustment effecting the richness of the engine mixture at high speeds only, whereas the needle valve |79 constitutes the low speed adjustment.

The carburetor shown in Fig. 3 is an extremely simple form of carburetor of a type suitable for use on the less expensive types of engine-driven lawn mowers. In such installations the supply tank is made relatively shallow so that the mixture variation between a full and nearly empty tank does not unduly affect the operation of the carburetor. Also, this tank is located immediately beneath the carburetor so that the overall fuel lift is maintained at a minimum.

In the better grade of lawn mowers and other small engine installations, the fuel tank is located above the carburetor and fuel runs by gravity from the fuel tank down into the carburetor. In utilizing this form of my carburetor in such an installation, a float mechanism would be interposed between the fuel supply line and the carburetor proper.

While I have illustrated only two forms of my invention, it is to be understood that my invention is not limited to the particular embodiments shown but may assume numerous other forms and includes all modifications, variations, and equivalents coming within the scope of the appended claims.

I claim:

1. In a carburetor, a casing having a choke bore and a throttle bore in axial alignment with the diameter of the choke bore being at least substantially equal to that of the throttle bore, a restriction between said bores, said choke bore being adapted to communicate on its inlet side with a source of air, and said throttle bore being adapted to communicate on its outlet side with the intake manifold of an internal combustion engine, a throttle valve in the throttle bore, a bypass passage around said restriction communieating at its ends with said choke and throttle bores, respectively, adjacent to the restriction, valve means biased to normally close said passage, said valve means being responsive to a pressure differential between said two bores corresponding substantially to full open throttle and less than normal engine load for said throttle opening, for opening said passage to bypass air around said restriction and thereby provide greater air flow between said two bores, and means for supplying fuel to air passing through said bores.

2. A carburetor as set forth in claim 1 in which the choke bore and throttle bore are substantially straight and in which the bypass passage is formed in the casing immediately adjacent to and parallel to said bores.

3. A carburetor as set forth in claim 1 in which said valve means is adjustable to thereby vary the pressure differential required to operate said valve.

4. A carburetor as set forth in claim 1 in which said two bores are substantially straight and in which said bypass passage is formed in said casing immediately adjacent to and parallel to said two bores, said valve means comprising a reed valve secured to said casing within said bypass passage, and a removable cover forming a wall of said passage and providing access to said reed valve.

References Cited in the le of this patent UNITED STATES PATENTS 

